The present invention relates generally to automatic controls for elevator doors, and particularly to a detection system for the recognition of obstacles.
There are many prior art devices for detecting or recognizing persons or objects within a given spatial region and are, therefore, applicable as safety devices. Examples of their use, for instance, are for the burglary proofing of rooms, as personal protection on dangerous machines, for the protection of working platforms, as well as anticollision protection on vehicles.
The prevailing state of technology of closure security devices for automatic elevator doors is characterized by the use of sensors of the most varied type of construction, such as for instance, mechanical feeler edges, light barriers, ultrasound devices, as well as capacitive and inductive measuring equipment. International patent application PCT/GB No. 82/00022 discloses a closure security device for elevator doors in which capacitive approach sensors with antennas are distributed across the door edges. The sensor signals emitted by the approach sensors are dependent on the ground capacitance of the pertinent antennas and are fed in pairs to differential amplifiers which generate error signals. The error signals control the door by way of an evaluating circuit. Obstacles in the region of the door, such as for instance a person or an object, change the ground capacitance of the sensor antennas in a distinct manner, so that the closing of the door can be prevented, stopped or reversed by least one of the error signals. In order that the differential amplifiers are operated within their regular working range during recognition of an obstacle, the sensors emit approximately equal sensor signals under obstacle-free conditions in spite of unequal earth capacitances caused for instance by the installation conditions. The sensors are balanced in pairs under obstacle-free conditions by compensators with incremental balancing memories and each sensor exhibits a special compensation input. In each case, a compensator is combined with a differential amplifier and one of the two associated sensors into a control circuit which balances the one sensor signal to the other until the pertinent error signal is zero. This compensation takes place in obstacle free conditions, for instance a door open one centimeter, and is triggered at the beginning of every door opening movement automatically by a microswitch.
In the above and similar electronically operated door security systems, the problem is to distinguish whether an error signal is due to an obstacle and must therefore be active in controlling the door, or whether it has been caused by an interference and should therefore be ignored for the purpose of door control. Such interferences result from the structural design of the elevator shaft, unevenly running and badly aligned doors, mechanical tolerances, as well as long term influences, such as dirt, humidity and mechanical deformations. For the solution to this problem the aforesaid patent relies on the knowledge that, under normal operating conditions of an elevator installation, obstacles such as persons and objects will generate rapidly variable error signals, while interferences (disturbing influences) will produce slowly changing error signals. The distinction between obstacles and interferences takes place therefore by pseudo-differentiation of the corresponding error signals; that is by comparison of the unretarded with the time-retarded error signal in an additional differential amplifier. Although the door security system designed in this way provides jamming protection, it is still accompanied by serious disadvantages.
One essential disadvantage is that the operation of the compensators is limited to a distance of a few centimeters from the opening of the door, so that the interferences (disturbing influences) are only compensated in this small door region and remain uncompensated in the greater remaining part of the door travel. Thus, the system performs a floor related point-wise balancing of the sensors rather than a compensation of the disturbing influences. This is not only an inefficient utilization of the time that the compensators are available, but the system is forced to differentiate signal-wise between obstacles acting on the door control and disturbing influences not acting on the door control. Since this operation takes place in a differentiating circuit, static obstacles, such as for instance a stationary person in the door region, have to be identified in an additional "static" circuit. This doubling of the evaluating circuitry is expensive and requires additional measures in order to decouple the static from the dynamic circuitry.
A further disadvantage is that disturbing influences in the elevator shaft between the floors can impair the function of the evaluating circuit, because the time constant of the delay element is matched to the door movements on a floor and not to the cabin movement in the elevator shaft. It is therefore necessary to initialize the timing unit at every floor stop, immediately prior to the door opening, by means of a microswitch. This complicates the function sequence for the recognition of the obstacle and reduces its reliability and safety. A further shortcoming is that the aforesaid obstacle recognition system does not have a memory, so that for instance an error signal due to a mechanical deformation and recognized as a disturbing influence has to be identified again and again for each door movement. Identifications already carried out therefore can not be used on subsequent door movements, and long-term influences such as contamination and humidity, which hardly change between the movements of the door, have to identified every time. Such an identification process poorly accommodates error signals, as encountered in normal elevator operation.